Question: Cody was $165\,\text{cm}$ tall on the first day of school this year, which was $10\%$ taller than he was on the first day of school last year. How tall was Cody on the first day of school last year?
Cody's height on the first day of school this year was $10\%$ taller than his height on the first day of school last year. He still had all $(100\%)$ of last year's height plus $10\%$ more. This year, he was $100\%+10\%=110\%$ of his height from last year. Percent means per hundred, so ${110\%}$ is equivalent to ${\dfrac{110}{100}}$ which is also equal to ${110\div 100}$. ${110\div 100 = 1.1}$ To find Cody's previous height, we need to answer, ${165\,\text{cm}}$ is ${110\%}$ of what height? We can rewrite that question as an equation. $\begin{array}{ccccc} {165\,\text{cm}}&\text{is}&{110\%}&\text{of}&\text{what height}\\\\ {165}&=&{1.1}&\times&? \end{array}$ Let's solve for the unknown height. $\begin{aligned} \dfrac{{165}}{1.1}&=\dfrac{{1.1}\times?}{1.1}\\\\ 150&=? \end{aligned}$ Cody was $150\,\text{cm}$ tall on the first day of school last year.